Removal of aqueous Fe2+ using MnO2–clinoptilolite in a batch slurry reactor: Catalyst synthesis, characterization and modeling of catalytic behavior

Zn2+, Fe2+, Cu2+, Mn2+, H+ Ion-exchanged and Raw Clinoptilolite Zeolite Catalytic Performance in the Propane-SCR-NOx Process: A Comparative Study

An investigation on the catalytic performance of various transition-metal ions-exchanged clinoptilolite zeolites in the propane selective catalytic reduction process of NOx (NO+NO2) is reported for the first time. The metallic ions include Zn2+, Fe2+, Cu2+ and Mn2+. The catalytic performance of these materials was compared with the proton form and natural clinoptilolite zeolites. Compared with the raw and H-form clinoptilolite, the ion-exchanged zeolites shift the temperature corresponding to the maximum conversion around 50 °C towards lower temperatures, irrespective of the type of used transition-metal used. The maximum conversion is substantially enhanced especially in the case of Cu2+ and Mn2+-exchanged zeolite. The enhanced activity is attributed to the creation of strong acidic sites, redox centers, enhanced specific surface area and residual extra framework Fe species. Ion-exchange with transition metals results in a distinct effect on the reduction of the CO concentration in the product gas stream. Cu2+ exchanged clinoptilolite resulted in the smallest outlet concentration of CO, i. e. about 81 % reduction with respect to the protonated zeolite form.

Reduction of nitrate by NaY zeolite supported Fe, Cu/Fe and Mn/Fe nanoparticles

Nano particles Fe, Cu/Fe and Mn/Fe supported on NaY zeolite (F@Y, CF@Y, and MF@Y) were prepared by two-step processes consisting of ion exchange and liquid-phase reduction. The characterization by XRD, SEM-EDX and BET-N₂ adsorption demonstrated that Fe, Cu/Fe and Mn/Fe nano particles were successfully loaded onto NaY zeolite and exhibited larger BET surface area compared to nano-Fe⁰ (nZVI). Laboratory experiments showed that nitrate removal by metals@Y in unbuffered conditions reached nearly 100% at a dosage of 4g/L after 6h of reaction. Moreover, the nitrate removal was not sensitive to the initial solution pH. Even at a high pH of 9.0, metals@Y exhibited nitrate reduction above 94%. CF@Y demonstrated high N₂ selectivity, due to the high content of Cu (20wt%) and Fe (41wt%) in CF@Y and the highly active metallic sites on its surface with positive charge. Kinetic data showed a good fit to a first-order kinetic model during early reaction times. A close fit to both a second-order and an nth-order kinetic model was shown for the whole of the reaction period. The data suggest that both liquid phase mass transfer and the intrinsic reaction rate control the process of nitrate reduction by metals@Y.